Peroxidases in roots and primary leaves of Phaseolus vulgaris copper and zinc phytotoxicity:: a comparison

The contribution of peroxidases was studied in roots and primary leaves of bean seedlings as a part of the defence mechanism against copper and zinc imposed oxidative stress. Based on the metal content of the different plant organs, copper was mainly stored in the roots, whereas zinc was readily transported to the upper ground parts. In the roots copper had an increasing effect on the capacities of guaiacol and syringaldazine peroxidases. A possible role for lignification in establishing an apoplastic transport barrier in roots is hypothesised. Zinc, on the other hand, had a limited impact on the root metabolism. Future studies should focus on other protection mechanisms in this plant organ. In the primary leaves, both elements had a pronounced (increasing) effect on the peroxidase activities. The data obtained in this study show that peroxidases contribute to the antioxidative defence of the primary leaves of 10 days old bean seedlings after application of both metals and that an interorgan signal transduction pathway is involved. It is pointed out that additional experimental approaches are necessary before the protection mechanism against different metals can be fully compared.